Thanks very much for the replies so far. I really do appreciate how you
lot get your teeth into an unusual problem!
But I misjudged the amount of detail that people might need in order to
give a helpful reply. My apologies for that - I was trying to spare you
all "the full half-hour". Well, here it comes...
This is a rather unusual application, and many of the normal electrical
wiring requirements do not apply.
I'm looking for about 1km of thin-ish solid copper wire, as cheap as
possible.
Yes, Andy, it is to make a ground mat for a radio aerial... well, four
aerials actually! This requires the wires to be laid out in a fairly
precise pattern of four radial fans, and the ends soldered to bare
copper "busbars".
BTDT before, but only on a smaller scale requiring much less wire. This
time I'm doing it at a new location and on a much bigger scale.
The amount of wire required - literally more than a kilometre - means
that (a) I'll have to buy it, and (b) paying the odd few pence more per
metre will add up to serious money.
The number of separate lengths of wires involved - approaching 200 -
means I have to think about easy "mass production" techniques. Many of
the things you wouldn't hesitate to do for a few tens of metres are
simply not on at the kilometre scale. Wire's too long; life's too short.
1. Solid, not stranded
That is an absolute requirement - please take my word for it. (At radio
frequencies, the resistance of stranded wire becomes much higher when
the strands corrode, as they inevitably will over the years. Solid wire
is much less affected.)
2. To be used as single wires, in lengths of typically 10m
3. Could be insulated or bare, tinned or not;
From the performance point of view, it makes no difference whether the
wire is insulated or not (see, I told you this was unusual).
but not enamelled (unless
the price was very, very right)
BTDT - enamelled is a pain to scrape and connect, especially when doing
it about 200 times, outdoors at ground level.
4. Strong enough to cope with being laid on the ground outdoors, and
then generally trodden on and mowed over
About 1.0-1.5mm diameter would probably be fine.
Sorry, Grunff, I may have misled you by not specifying the kind of
surface. On grassy land, 1.5mm diameter copper is plenty strong enough
for the basic radial wires - strong enough to trip someone up, and it
will even stop a rotary mower (it cuts the wire, but the wire wins in
the end, by strangulation).
The trick when laying wires on grass is to mow the grass very short
first. Then lay the wires along the ground, heel down any sticking-up
loops, or pin them down with thicker wire 'staples'... and then simply
leave them. Just carry on mowing a bit higher than usual (which is where
you find any loops that you didn't pin down properly) and within a year
the wires will have disappeared under the root mat. It's quite
remarkable. Within two years, you'll even have to search for half-inch
cables.
5. Thin enough to be cheap.
As I said, on this scale the price per metre of wire really does matter
- especially bearing in mind it's only for a hobby. Each extra penny per
metre becomes another 10 quid on the total cost.
Dave said:
You need to specify either cross sectional area, SWG, or what current it
has to carry.
I'd hoped to get away without having to go into details, Dave... but
judging by some of the questions we get on here, you were quite right to
ask :-)
For this unusual application, most of the normal electrical wiring
factors don't matter at all. It all comes down to mechanical strength,
and price.
Single core insulated for electronic stuff is available from RS Components
etc. Go up to normal mains - ie 1mm/sq and above and you'll get it at any
electrical wholesaler.
If buying at normal catalogue prices, I'd rather spend all the money on
copper than on insulation that isn't needed. However, plain bare solid
copper seems to be the province of "instrument wire" suppliers, and is
sold at a huge premium compared with the copper content of say T&E.
Single core is used in conduit, etc.
Stranded, alas. That is the one definite no-no for this particular
application.
Andy said:
Or get some 7-strand conduit wire (say 10 or 16 mm^2) and strip out
the strands.
Because of the total length of wire involved, I'm afraid that would be
far too labour-intensive. The same would apply to options such as
stripping down scrap T&E. It's got to be some kind of wire that allows
an easy "mass production" technique.
Tricky... but I really do appreciate your help and good thinking.
--
Ian White
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